1. Technical Field
The present invention relates to a resonator having a thickness shear vibration mode as the main vibration, and particularly to a vibrating element having a so-called inverted mesa structure, a resonator, and an electronic device, an electronic apparatus, and a mobile object using such a resonator.
2. Related Art
An AT cut quartz crystal resonator is a resonator in which the main vibration mode which is excited is a thickness shear vibration, and since it is appropriate for miniaturization and increases in frequency, and presents a cubic curve with an excellent frequency-temperature characteristic, it has a wide variety of applications in piezoelectric oscillators and electronic apparatuses.
JP-A-2004-165743 (patent literature 1) discloses an AT cut quartz crystal resonator of a so-called inverted mesa structure that includes a recess on a portion of the main plane and is designed to achieve high frequency. The length of the Z′-axis direction of a quartz crystal substrate is set to be longer than the length of the X-axis direction, and a so-called Z′-long substrate is used.
JP-A-2009-164824 (patent literature 2) discloses an AT cut quartz crystal resonator of an inverted mesa structure in which thick support sections (thick sections) are continuously formed respectively on three sides of a thin rectangular vibrating section and one side of the thin vibrating section is configured to be exposed. Furthermore, a quartz crystal resonator element is an in-plane rotation AT cut quartz crystal substrate in which the X-axis and the Z′-axis of the AT cut quartz crystal substrate is rotated in the range of −120° to +60° around the Y′-axis respectively, and has a structure (multi-cavity structure) excellent in securing a vibration area and mass-production.
JP-A-2006-203700 (patent literature 3) and JP-A-2002-198772 (patent literature 4) disclose an AT cut quartz crystal resonator of an inverted mesa structure in which thick support sections are continuously formed respectively on three sides of a thin rectangular vibrating section and one side of the thin vibrating section is configured to be exposed, and in a quartz crystal resonator element, the length of a quartz crystal substrate in the X-axis direction is longer than the length thereof in the Z′-axis direction, and a so-called X-long substrate is used.
JP-A-2002-033640 (patent literature 5) discloses an AT cut quartz crystal resonator of an inverted mesa structure in which thick support sections are continuously formed respectively on two adjacent sides and a thick section having an L-shape in a plan view is provided in a thin rectangular vibrating section, and two sides of the thin vibrating section are configured to be exposed. In a quartz crystal substrate, a Z′-long substrate is used.
However, in JP-A-2002-033640 (patent literature 5), in order to obtain the L-shaped thick section, the thick section is cut out along a line α and a line β as described in FIGS. 1C and 1D of JP-A-2002-033640, but since cutting is performed on the premise of cutting using a mechanical process such as dicing, or the like, there are problems in that damage such as chipping, cracking, or the like is inflicted on a cut surface, and an ultra-thin section is broken. In addition, other problems occur such as the generation of unwanted vibration that may cause spurious vibrations in a vibration area, an increase of a CI value, or the like.
JP-A-2001-144578 (patent literature 6) discloses an AT cut quartz crystal resonator of an inverted mesa structure in which a thick support section is continuously formed on one side only of a thin vibrating section and three sides of the thin vibrating section are configured to be exposed.
JP-A-2003-264446 (patent literature 7) discloses an AT cut resonator of an inverted mesa structure that is designed to achieve high frequency by forming a recess so as to oppose both main planes that are front and rear surfaces of a quartz crystal substrate. For the quartz crystal substrate, an X-long substrate is used, and a configuration is proposed in which excitation electrodes are provided in regions where flatness of a vibration area formed in the recess is secured.
With regard to a thickness shear vibration mode in which excitation is shown in a vibration area of an AT cut quartz crystal resonator, it is known that the vibration displacement distribution has an ellipsoidal shape having a long diameter in the X-axis direction due to anisotropy of an elastic constant. JP-A-2-079508 (patent literature 8) discloses a piezoelectric resonator in which a thickness shear vibration is excited with a pair of ring-shaped electrodes arranged on both the front and rear surfaces of a piezoelectric substrate so as to be symmetric in terms of front and rear sides. The difference between an outer circumferential diameter and an inner circumferential diameter of the ring-shaped electrodes is set so that the ring-shaped electrodes are excited only in a symmetric zero-order mode and seldom excited in other inharmonic higher-order modes.
JP-A-9-246903 (patent literature 9) discloses a piezoelectric resonator in which the shapes of a piezoelectric substrate and excitation electrodes provided on the front and rear surfaces of the piezoelectric substrate is set to be ellipsoidal shapes.
JP-A-2007-158486 (patent literature 10) discloses a quartz crystal resonator in which the shapes of both ends of a quartz crystal substrate in the long side direction (X-axis direction) and both ends of electrodes in the X-axis direction are set to be semi-elliptical shapes, and the ratio of the major axis to the minor axis (major axis/minor axis) of the ellipse is set to 1.26.
JP-A-2007-214941 (patent literature 11) discloses a quartz crystal resonator in which elliptical excitation electrodes are formed on an elliptical quartz crystal substrate. The ratio of the major axis to the minor axis is desirably 1.26:1, but when unevenness in manufacturing dimensions, or the like is considered, a ratio in the range of about 1.14 to 1.39:1 is effective.
JP-UM-A-61-187116 (patent literature 12) discloses a piezoelectric resonator that is configured to include a cutout or a slit between a vibrating section and a support section so as to further improve the energy trapping effect of a thickness shear piezoelectric resonator.
When miniaturization of a piezoelectric resonator is designed to achieve, there is a case where deterioration in electric characteristics or degradation of a frequency aging characteristic are caused due to residual stress caused by an adhesive. JP-A-9-326667 (patent literature 13) discloses a quartz crystal resonator in which a cutout or a slit is provided between a vibrating section and a support section of a flat rectangular AT cut quartz crystal resonator. It is said that the use of such a configuration can hinder residual stress from expanding to a vibration area.
JP-A-2009-158999 (patent literature 14) discloses a resonator in which a cutout or a slit is provided between a vibrating section and a support section of an inverted mesa type piezoelectric resonator in order to ease (alleviate) mounting strain (stress).
JP-A-2004-260695(patent literature 15) discloses a piezoelectric resonator in which conduction of electrodes on the front and rear surfaces is secured by providing a slit (through hole) in a support section of an inverted mesa type piezoelectric resonator.
JP-A-2009-188483 (patent literature 16) discloses a quartz crystal resonator that suppresses a higher-order contour unwanted mode by providing a slit in a support section of a thickness shear vibration mode AT cut quartz crystal resonator.
In addition, JP-A-2003-087087 (patent literature 17) discloses a resonator that suppresses spurious vibrations by providing a slit in a continuous section of a thin vibrating section and a thick holding section, in other words, in a residual section having an inclined surface, of an inverted mesa type AT cut quartz crystal resonator.
In recent years, demand for miniaturization, high frequency, and high performance of a piezoelectric device has intensified. However, when miniaturization and high frequency are intended, it is clear that there is a problem in that, with regard to a piezoelectric resonator of the above-described configuration, a CI value of the main vibration, a ratio of CI values of proximate spurious vibrations (=CIs/CIm, wherein CIm is a CI value of the main vibration, and CIs is a CI value of spurious vibrations, and a standard example is 1.8 or higher) and the like do not satisfy the demands. Particularly, when a frequency is a high frequency of several hundred MHz, the thickness of an electrode film of an excitation electrode formed in a piezoelectric vibration element and a lead electrode are problematic. When only the main vibration of the piezoelectric vibration element is intended to be in a trapping mode, there are problems in that the electrode film is thin, ohmic loss arises, and the CI value of the piezoelectric vibrating element increases.
In addition, when the thickness of the electrode film is thickened in order to prevent ohmic loss of the film, there is a problem in that many inharmonic modes other than the main vibration are shifted to trapping modes, and thus, the ratio of CI values of proximate spurious vibrations is not attained.